Due to the spread of expressway network and the increase in running speed of cars, especially passenger cars, radial tires having a steel cord belt disposed radially outside the radial carcass have been widely used as tires suitable for high-speed running. In such a radial tire, however, when running at high speed, the centrifugal force accompanying the high speed rotation of tire sometimes lifts the belt to cause separation of the belt edges from the surrounding rubber. Especially when cut-end plies are used for the belt, the above-mentioned rubber separation is further promoted by poor adhesion between the cut-ends and the rubber.
In order to prevent the rubber separation at the edges of the belt ply to thereby improve high speed durability, as shown in FIG. 4 to 8, various means have been proposed. In FIG. 4, an a edge band B made of organic fiber cords is disposed on the upper surface of the edge portion of the belt A. In FIG. 5, two layers of the edge bands B are disposed. In FIG. 6, a full band C extending over the entire width of the belt A is disposed in addition to the edge band B. In FIG. 7, only the full band C extending over the entire width of the belt A is provided. In FIG. 8, two layer of the full bands C extending over the entire width of the belt A are disposed.
Considering the high speed durability, the tire shown in FIG. 5 having two layer of the edge bands B is superior to the one shown in FIG. 4 having a single layer of the edge band B. Furthermore, the tire shown in FIG. 6 having both the edge band B and full band C extending over the entire width is superior in the high speed durability to the one shown in FIG. 7 provided with a single layer of the full band C.
In the tire shown in FIG. 5 having two layers of the edge bands B, however, difference in stiffness tends to be generated between the tire crown and the tire shoulders, that is, the belt edge portions, and the difference causes uneven distribution of the ground pressure on the tread. As a result, the steering stability, particularly the steering stability at high speed is deteriorated and uneven wear tends to occur. In the tire shown in FIG. 8 using two layers of the full bands C covering the entire surface of the belt A, there is no difference in stiffness. In spite of the rigid steel cord belt A, the tread stiffness is decreased by the softer organic fiber full band C, and the steering stability at high speed is impaired. The tire shown in FIG. 7 has a similar problem.
Still furthermore, in the Japanese Patent Application KOKAI No. 58-61005, as shown in FIG. 9, an edge band D is disposed between the carcass and the belt A in addition to the edge band B disposed radially outside the belt A.
In this tire, however, the upper and lower edge bands B and D are inclined largely at 8 to 15 degrees in reverse directions with respect to the tire equator, and by such construction, tightness of the bands in the circumferential direction of the tire can not be obtained. Therefore, such edge bands can not work effectively as a tensile member.
On the other hand, a reduction in uneven wear and an improvement in wear resistance are required as tire characteristics together with the steering stability and the high speed durability as stated above. For that purpose, it is preferable to even out the distribution of the ground pressure at the tread face.
The above-mentioned edge bands, however, tend to make uneven the distribution of the ground pressure. The edge bands increase the stiffness of the tire shoulder portions, and accordingly the amount of inflation at the shoulder portions is relatively reduced in comparison with the crown portion. As a result, the ground pressure becomes high in the crown portion.